This invention relates to an improved knife-holder for wood chippers of the type having a series of substantially radially positioned knives mounted on a rapidly rotatable disc. The improved knife-holder completely eliminates the recessed and tapped holes used for attaching a counter knife to the holder and, additionally, completely eliminates the counter-knife itself, thereby creating a much-improved holding power in the knife-holder assembly. The instant invention effectively combines the counter-knife and knife holder currently used into one solid unit.
Conventional wood chippers for reducing slabs, logs or even entire trees to wood chips generally employ a rotatably mounted cutting disc. The cutting disc is usually formed from a mild steel and may be approximately five inches thick. A plurality of cutting blades or knives are mounted adjacent apertures on the cutting discs to be rotated therewith. The rotating disc is mounted on a base structure and typically includes a wear plate mounted to the face of the disc. The cutting knives which may be from twelve to thirty-six inches in length are secured to the aperture sides of the disc by a knife holder, counter knife and knife clamp, all of which are bolted directly or indirectly to the rotating disc. A housing surrounds the disc and includes an opening through which the wood to be chipped may be passed. The opening is covered by a spout which terminates in a feed plate adjacent an anvil. During rotation of the disc, the cutting knives are passed adjacent the face of the anvil and at such an angle so as to draw in the raw material to produce wood chips which are expelled through an exhaust chute usually at the periphery of the housing. The wood chips are generally employed in the paper mill industry.
The anvil, the feed plate, the wear plate mounted on the rotating disc, the knife clamp, the counter knife, and the knife holder are all subjected to wear due to the extreme frictional and impact forces incurred during operation. Since close tolerances are involved with respect to the clearance between the stationary and the rotating parts and due to the relatively high rpm at which the massive steel disc rotates, these wear parts must be replaced quite frequently to maintain efficient operation of the chipper.
Due to the relatively high cost of each of these individual wear parts, attempts have been made to repair the worn parts for reuse. All of these prior attempts to repair or resurface the wear parts have been to varying extents unsuccessful for various reasons. Moreover, the current design of wood chippers employing a knife holder and counter knife allows small wood chips, splinters and wood dust to become lodged or packed between the counter knife and knife holder and inside the head of the Allen screws which typically hold the counter knife to the knife holder and around the screws themselves. This not only makes it difficult to change the counter knife but also adversely effects the alignment of the cutting tool.
Another problem with the current design is that sufficient strength to properly position the cutting knife is difficult to achieve through the use of a counter knife in the knife holder assembly. This exacerbates the problem of dust and chip particles packing between the holder and counter knife and between the counter knife and chipper knife. When this occurs, a safety hazard results. Continued use of the machine can irreparably damage the counter knife, chipper knife and knife holder. Moreover, damage to other parts of the machine can occur.
It is therefore an object of the present invention to provide an improved knife holder assembly which is simple and durable in construction and highly efficient in use, and which solves the problems caused by the use of the conventional knife holder which incorporates a counter knife in its design.
The instant invention substantially reduces the cost of the knife holder assembly. The invention eliminates the necessity to mill out a recess for the counter knife and the drilling and tapping of holes to affix the counter knife to the knife holder. Also, the invention eliminates the bolts holding the counter knife to the knife holder and the counter knife itself. Because all of the foregoing parts have to be machined for close tolerances to insure proper clearances between such parts and other moving parts of the machine and between such parts themselves, the elimination of the counter knife eliminates the necessity of insuring that these tolerances are met with respect to an additional wear part. The present invention not only helps eliminate these costs but also eliminates the necessity of replacing the knife holder itself as often as is done so now. Furthermore, because the instant invention incorporates the practice of hard surfacing the wear surface of the knife holder, the new assembly will last many times longer than that presently used. Currently, the counter knife and the knife holder itself wear considerably during operation.
The present invention will eliminate all of the foregoing problems because it is manufactured without the counter knife, thereby eliminating the need for a machined slot and clamping screws to secure the counter knife. This allows for a more durable, more secure, safer and less expensive knife holder assembly. When the instant knife holder does need replacement, the replacement thereof is much easier and can be performed more quickly than replacing the currently available knife holder assembly which includes a counter knife.